import cv2
import numpy
import time

class CaptureManager:

    def __init__(self, capture, previewWindowManger = None, 
            shouldMirrorPreview = False):
        self.previewWindowManager = previewWindowManger
        self.shouldMirrorPreview = shouldMirrorPreview

        self._capture = capture
        self._channel = 0
        self._enteredFrame = False
        self._frame = None
        self._imageFilename = None
        self._videoFilename = None
        self._videoEncoding = None
        self._videoWriter = None

        self._startTime = None
        self._frameElapsed = 0
        self._fpsEstimate = None

    @property
    def channel(self):
        return self._channel

    @channel.setter
    def channel(self, value):
        if self._channel != value:
            self._channel = value
            self._frame = None

    @property
    def frame(self):
        if self._enteredFrame and self._frame is None:
            _, self._frame = self._capture.retrieve()
        return self._frame

    @property
    def isWritingImage(self):
        return self._imageFilename is not None

    @property
    def isWritingVideo(self):
        return self._videoFilename is not None

    def enterFrame(self):

        assert not self._enteredFrame, \
            "previous enterFrame() had no matching exitFrame()"
        
        if self._capture is not None:
            self._enteredFrame = self._capture.grab()

    def exitFrame(self):
        if self.frame is None:
            self._enteredFrame = False
            return
        
        if self._frameElapsed == 0:
            self._startTime = time.time()
        else:
            timeElapsed = time.time() - self._startTime
            self._fpsEstimate = self._frameElapsed / timeElapsed
            
        self._frameElapsed += 1

        if self.shouldMirrorPreview:
            mirroredFrame = numpy.fliplr(self._frame).copy()
            self.previewWindowManager.show(mirroredFrame)
        else:
            self.previewWindowManager.show(self._frame)
        
        if self.isWritingImage:
            cv2.imwrite(self._imageFilename, self._frame)
            self._imageFilename = None
        

        self._writeVideoFrame()

        self._frame = None
        self._enteredFrame = False
    
    def writeImage(self, filename):
        self._imageFilename = filename

    def startWritingVideo(self, filename, 
            encoding = cv2.VideoWriter_fourcc('I', '4', '2', '0')):
        
        self._videoFilename = filename
        self._videoEncoding = encoding

    def stopWritingVideo(self):
        self._videoFilename = None
        self._videoEncoding = None
        self._videoWriter = None

    def _writeVideoFrame(self):
        if not self.isWritingVideo:
            return

        if self._videoWriter is None:
            fps = self._capture.get(cv2.CAP_PROP_FPS)
            if fps == 0.0:
                if self._frameElapsed < 20:
                    return
                else:
                    fps = self._fpsEstimate
            size = (int(self._capture.get(cv2.CAP_PROP_FRAME_WIDTH)),
                    int(self._capture.get(cv2.CAP_PROP_FRAME_HEIGHT)))
            self._videoWriter = cv2.VideoWriter(
                self._videoFilename, self._videoEncoding, fps, size)
        
        self._videoWriter.write(self._frame)


class WindowManager:

    def __init__(self, windowName, keypressCallback = None) -> None:
        self.keypressCallback = keypressCallback

        self._windowName = windowName
        self._isWindowCreated = False

    @property
    def isWindowCreated(self):
        return self._isWindowCreated
    
    def createWindow(self):
        cv2.namedWindow(self._windowName)
        self._isWindowCreated = True

    def show(self, frame):
        cv2.imshow(self._windowName, frame)

    def destroyWindow(self):
        cv2.destroyWindow(self._windowName)
        self._isWindowCreated = False

    def processEvents(self):
        keycode = cv2.waitKey(1)
        if self.keypressCallback is not None and keycode != -1:
            keycode &= 0xFF
            self.keypressCallback(keycode)
